The present invention relates to a stabilized sodium percarbonate composition, particularly a stabilized sodium percarbonate composition suitable for use as a bleaching agent in detergents, etc.
Sodium percarbonate is generally used widely as a bleaching agent, a detergent, or a sterilizer. Sodium percarbonate as a bleaching agent is superior in solubility at low temperatures, exhibits a high bleaching effect, and is a stable compound in an ordinary perserved state. However, sodium percarbonate is disadvantageous in that it is unstable when preserved in a high humidity condition or when incorporated in a detergent. As a household detergent, a product containing a predetermined certain amount of sodium percarbonate as a bleaching agent is particularly preferred. When incorporated in a detergent, however, sodium percarbonate loses its stability upon contact with a zeolite which is used as a builder or with water contained in a very small amount in the detergent, resulting in that not only the sodium percarbonate no longer exhibits the bleaching effect but also there is fear of the detergent losing its effect. Various proposals have heretofore been made for solving these problems. For example in Japanese Patent Publication No. 56167/1988 there is disclosed a method wherein sodium percarbonate is coated with magnesium sulfonate or magnesium salt of sulfuric ester; in Japanese Patent Publication No. 57362/1988 there is disclosed a method wherein sodium percarbonate is coated with such magnesium salt plus sulfate or hydrochloride of an alkali or alkaline earth metal; in Japanese Patent Laid-Open No. 118606/1085 there is disclosed a method wherein sodium percarbonate is coated with boric acid or a partially neutralized borate and a water repellent; in Japanese Patent Laid-Open No. 194000/1984 a method wherein sodium percarbonate is coated with a borate and a magnesium compound; and in Japanese Patent Laid-Open No. 129500/1975 a method wherein sodium percarbonate is coated with a mixture of a surfactant and a water-insoluble compound which is compatible with the surfactant. All of these methods intend to prevent sodium percarbonate from coming into contact with detergent ingredients and to stabilize it by coating it with specific chemical substances. According to these conventional methods, however, when the sodium percarbonate thus coated is preserved in a high humidity condition or when incorporated in a detergent, the stabilization effect is not attained at all to a satisfactory extent in practical use.
It is the object of the present invention to solve the above-mentioned problem. The present inventors found that the aforesaid problem which had not been solved by the prior art could be overcome by incorporating in sodium percarbonate a mono- or dicarboxylic acid having not less than four carbon atoms or a salt thereof add a sulfate, nitrate or silicate of an alkali metal or alkaline earth metal. In this way we reached the present invention.